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Date: Tue, 3 Sep 2024 07:18:07 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: Claudiu.Beznea <claudiu.beznea@...on.dev>, Ulf Hansson
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Subject: RE: [PATCH 00/16] Add initial USB support for the Renesas RZ/G3S SoC

Hi Claudiu,

> -----Original Message-----
> From: Biju Das
> Sent: Monday, September 2, 2024 11:48 AM
> Subject: RE: [PATCH 00/16] Add initial USB support for the Renesas RZ/G3S SoC
> 
> Hi Claudiu,
> 
> > -----Original Message-----
> > From: claudiu beznea <claudiu.beznea@...on.dev>
> > Sent: Monday, September 2, 2024 11:41 AM
> > Subject: Re: [PATCH 00/16] Add initial USB support for the Renesas
> > RZ/G3S SoC
> >
> >
> >
> > On 02.09.2024 12:18, Biju Das wrote:
> > >>>>> Do you have any plan to control this power transitions(ALL_ON to AWO and vice versa) in linux?
> > >>>> As you know, the RZ/G3S USB PM code is already prepared. This is
> > >>>> also configuring these signals when going to suspend/exiting from resume.
> > >>>> W/o configuring properly these signals the USB is not working after a suspend/resume cycle.
> > >>> One option is to handle SYSC USB PWRRDY signal in TF-A, if you
> > >>> plan to handle system transitions
> > >> there??
> > >>
> > >> As I mentioned, the settings in these registers may be changed by
> > >> intermediary booting
> > applications.
> > >> Depending on that, Linux need to control it also on probe for USB
> > >> to work (it should be the same with PCIe, these signals seems similar from HW manual
> description).
> > > You mean system transition settings will be override by U-boot, so Linux needs to restore it
> back??
> >
> > It was talking about booting...
> 
> I am also referring to boot. Boot starts with TF-A and it has a system state.
> 
> >
> > You proposed to handle SYSC signals from TF-A in a discussion about system power transitions:
> >
> > "One option is to handle SYSC USB PWRRDY signal in TF-A,  if you plan to handle system transitions"
> >
> > (I was guessing the "system transition" statement there refers to
> > power states transitions, ALL_ON <->
> > AWO/VBAT)
> 
> That is correct.
> 
> >
> > and I gave the booting process as a counter example: if we handle it
> > in TF-A it may not be enough as these signals might be changed by intermediary booting applications
> (e.g., U-Boot).
> 
> Why should U-boot override, system state signals such as USB PWRREADY? Can you please give an example.
> 
> >
> > To conclude, there are 3 scenarios I see where these signals need to
> > be
> > handled:
> > 1/ booting
> > 2/ suspend to RAM
> > 3/ driver unbind/bind
> 
> --> It should be OK as linux is not handling USB PWRREADY signal.
> 
> >
> > In case of booting: if we have TF-A to set signals there might be
> > intermediary booting applications (e.g. U-Boot) that set these signals
> > also. If it leaves it in improper state and Linux wants to use USB then the USB will not work (if
> Linux doesn't handle it).
> 
> That is the problem of U-boot. U-boot should not override system state signals such as USB PWRREADY.
> 
> >
> > In case of suspend to RAM: as TF-A is the only application in the
> > suspend to RAM chain, it should work handling it in TF-A.
> 
> That is correct, TF-A should handle based on system state.
> 
> >
> > In case of unbind/bind: currently we don't know if these signals
> > introduces any kind of power saving so asserting/de-asserting them in Linux may be useful from this
> perspective, if any.
> 
> These are system signals, according to me should not be used in unbind/bind.
> 
> I may be wrong.

Just to add the below are the 4 system states (power mode) for this LSI.

If I understand correctly, we need to configure USB PWRRDY signal
only when there is a transition from ALL_ON to AWO mode and vice versa.
as you see on AWO mode only CM-33 is active.

• ALL_OFF mode: All CPUs and peripheral modules can not be worked.
• ALL_ON mode: All CPUs and peripheral modules can be worked.
• AWO mode: Cortex-M33 and peripheral modules in PD_VCC and PD_VBATT domain can be worked.
• VBATT mode: Only RTC, tamper detection and backup registers can be worked.

System manager which is controlling both CA-55 and CM-33, will set USB PWRRDY signal
based on system state.

Since we don't have system manager for controlling both CA-55 and CM-33
Probably from CA-55 perspective, TF-A should be sufficient.

During boot clr USB PWR READY signal in TF-A.
STR case, suspend set USB PWR READY signal in TF-A.
STR case, resume clr USB PWR READY signal in TF-A.

I am not expert in this area. I may be wrong.

Maybe we need to get an opinion from Power experts in Linux.

Cheers,
Biju

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